Filament tensioning device for electron gun structure



C. F. STERZL Jan. 24, 1967 FILAMENT TENSIONING DEVICE FOR ELECTRON GUN STRUCTURE 4 Sheets-Sheet 1 Filed Jan. 7, 1963 INVENTOR. CARL F. STERZL ATTORNEYS Jan. 24, 1967 c. F. STERZL 3,300,

FILAMENT TENSIONING DEVICE FOR ELECTRON GUN STRUCTURE Filed Jan. 7, 1963 4 Sheets-Sheet 2 Fig-3 INVENTOK Q CARL F. STERZL WWW ATTOR NEYS Jan. 24, 1967 c, F. STERZL 3,300,676

FILAMENT TENSIONING DEVICE FOR ELECTRON GUN STRUCTURE Filed Jan. '7, 1963 4 Sheets-Sheet 3 a w W s j d L T b l m w WM 74 w W I INVENTOR. CARL F. STERZL.

BY W 3 6 ATTORNEYS C. F. STERZL Jan. 24, 1967 FILAMENT TENSIONING DEVICE FOR ELECTRON GUN STRUCTURE Filed Jan. 7, 1965 4 Sheets-Sheet 4 INVENTOR CARL F. STERZL ATTORNEYS United States Patent 3,300,676 FILAMENT TENSIONING DEVICE FOR ELEC- TRON GUN STRUCTURE Carl F. Sterzl, Alamo, Califl, assignor to Staulfer Chemical Company, New York, N.Y., a corporation of Delaware Filed Jan. 7, 1963, Ser. No. 249,933 4 Claims. (Cl. 313-278) This invention relates to electron gun structures in which an elongate filament is held under continual tension.

In electron beam melting and casting and annealing furnaces electron guns often are used having an elongate filament which operates as a thermionic cathode. Such gun construction must in some way account for the fact that the elongate filament expands and contracts under various temperature conditions. If the filament should expand and sag, its relative position with respect to the focus electrodes and accelerating anode may change to alter the shape and direction of the electron beam issuing from the gun. In guns utilizing a plurality of closely spaced filaments there is the possibility of a short being caused between adjacent filaments if one or more of the filaments should sag.

The principal object of this invention is to provide in an elongate filament electron gun provision for continually tensioning the filament to prevent displacement of the filament element in which a novel weighted means applies continual tension to the filament at all operating temperatures.

One of the features and advantages of this invention lies in the fact that the amount of tension applied to the filament by the weight is substantially unaffected by filament expansion and the repeated temperature changes occurring over an extended period of time.

Another object of this invention is to provide a novel filament structure wherein tension applying weight is rotatably supported on a horizontal axis below and to one side of the weight center before the filament connected thereto expands. As the filament expands the weight is lowered and moved horizontally away from the horizontal axis thereby to increase the tension on the filament.

Still another object of this invention is to provide such a gun structure in which the tensioning weight means lies in the same plane as the filament and substantially entirely between the ends of the filament. In this manner no appreciable length is added to the gun structure by the tensioning means.

Other objects of the present invention will become apparent upon reading the following specification and referring to the accompanying drawings in which similar characters of reference represent corresponding parts in each of the several views.

In the drawings:

FIG. 1 is an elevational view of a preferred embodiment of an electron gun structure for an electron beam furnace, portions of the gun being shown in the phantom.

FIG. 2 is a transverse cross-sectional view of the structure shown in FIG. 1 taken along the line 2-2 looking in the direction of the arrows.

FIG. 3 is a side view, partially broken away, of the structure of FIG. 1 taken along the line 33 looking in the direction of the arrows.

FIG. 4 is a schematic view illustrating the manner in which the electron gun shown in FIGS. 1-3 can be utilized.

FIG. 5 is a schematic view illustrating the manner in which the gun structure shown in FIGS. 6 and 7 can be utilized.

FIG. 6 is a longitudinal side view, partially in section,

3,300,676 Patented Jan. 24, 1967 of another gun structure embodying this invention and adapted for use in an annealing furnace.

FIG. 7 is a transverse cross-sectional view of the structure shown in FIG. 6 taken along line 7-7 looking in the direction of the arrows.

Referring now to the drawings and with particular reference to FIGS. 1-3, there is shown an electron gun 10 which includes a horizontal elongate filament 11 bent double at its mid portion 11a to form a hair pin shaped filament. Each of the free ends of the hair pin is secured such as, for example, by a set screw in a support arm 12 with the end portion of the filament 11 protruding out wardly from the support arm for connection to a filament lead (not shown). The support arms 12 are secured side by side on the upper shelf 13 of the two shelves 13 and 14 which are supported between two vertical spaced apart plates 15 and 16, the tops of the plates 15 and 16 projecting into the region adjacent the filament 11 and serving as focus electrodes. One support arm 12 is insulated from the shelf on which it is mounted so that a current can be passed through the filament 11 to heat same.

The bend 11a in the filament 11 is positioned in a groove near one end of a tensioning lever arm 17, and adjacent this arm 17 a bus bar 18 joins the filament legs to hold the filament on the arm 17 and prevent current from passing through the bend. Below the groove therein the tensioning arm 17 is rotatably mounted substantially at its mid portion on a horizontal pin 19 held in two arms on a bracket 20 which is carried from the upper shelf 13.

The bottom surface of the lower shelf 14 is supported on top of insulators 21 the bottom of which are carried on the base of a gun housing structure 22. This gun housing structure 22 is maintained at a positive potential with respect to the filament and focus electrode structure and is provided with a side extension 23 which is spaced from the focus electrode structure and projects into the region near the filament 11 to serve as an anode. The anode, focus electrodes, and the filament are positioned with respect to one another so as to produce an electron beam of desired shape directed in the required direction. Cooling means such as water tubing 24 is provided on the anode to cool that structure and prevent emission therefrom.

Supported from the top surface of the lower shelf 14 substantially midway thereof is another mounting bracket 25 which holds a pin 26 aligned substantially horizontal and parallel to the pin 19. Rotatably mounted on this pin 26 is a weight mounting block 27 provided with rigid weight support arms 28 extending therefrom in a direction away from the filament tensioning arm 17, the block 27 and arms 28 forming a lever arm. A weight 29 is secured to the extended ends of the support arms 28, and a connecting rod 30 connected the weight mounting block 27 to the lower portion of the filament tensioning arm 17 whereby the moment of the weight 27 about the pin 26 applies tension to the connecting rod 27 and in turn to the filament 11 through the intermediary lever action of the tensioning arm 17.

In order to avoid shorting out the last half of the filament 11 the brackets 20 and 25 mounting the arm 17 and block 27 respectively, are supported from the upper and lower shelves in an insulated manner.

As is evident from the above the weight 29 applies a continual tension to the filament 11 thereby preventing .filament sag which would result in misalignment of the According to the preferred embodiment of this invention, before the filament 11 is heated up and expands the weight 29 connected to the rigid arms 28 is positioned vertically above the pin 26 so that as the filament 11 initially expands, thereby lowering and moving the weight 29 horizontally away from the pin 26, the moment of the weight 29 about the pin 26 increases to increase the tension on the filament 11. In previous gun structures employing spring tensioning means the tension on the filament always decreased as the filament expanded.

As described above, the weight 29, its rotating support structure, and the structure which connects the weight 29 to the filament 11 for applying tension thereto are all positioned in the vertical plane passing through the filament substantially entirely within the length of the folded filament whereby the gun structure need be no longer than the length of the folded filament.

The tensioning arm 17 need not be rotated exactly at its mid-portion on the pin 19. By adjusting this position of rotation the lever action can be changed to select the desired mechanical advantage and weight movement limits.

Referring now to FIG. 4 the electron gun described with reference to FIGS. 1-3 is conveniently utilized as a transverse gun in an electron beam furnace utilized for electron beam melting and casting. The electron gun 10 is positioned below the top surface of a mold 31 in which a material is positioned for melting and casting. The electron ribbon beam 32 from the electron gun 10 is directed upwardly into a magnetic field 33 which is arranged transversely to the direction of the electron beam. The magnetic field which in FIG. 4 is indicated as directed into the plane of the paper exerts a force on the electrons directed thereinto causing the electron beam 32 to travel an accurate path and fall on the material in the mold 31. The electron beam furnace is continually pumped to a low pressure by a pump 34.

Referring now to FIG. 5 there is shown in schematic form an electron gun 40 for use in an annealing furnace. The electron gun 40 generates an electron ribbon beam 41 onto the material 42 being processed.

Referring now more particularly to FIGS. 6 and 7 showing an electron gun 40 for use in such an annealing furnace two elongate filaments 43 are positioned in a colinear spaced apart manner. The end of each filament furthest from the other filament is rigidly held by means of a set screw on one end of a metalli support post 44. The other end of the support posts 44 are supported an insulated manner on the inside top surface of an elongate inverted channel member 45 substantially midway between the sides thereof. A longitudinal opening 46 is provided in the bottom surface of the channel member 45 and the filaments 43 are positioned adjacent this opening 46 for directing the electron beam 41 therethrough, the channel member 45 serving as a focus electrode for the gun 40.

The ends of the filaments 43 which are adjacent one another are secured by means of set screws in rod stubs 43a mounted in one end of weight support lever arms 47 which protrude substantially vertically upwardly through the channel member 45 and are rotated about horizontal axes 48 generally midway thereof. A weight 49 is supported from the other end of each of the support arms 47 by a substantially horizontally aligned connecting rod 50 which is directed in the same direction from the horizontal axis 48 as is the filament 43. By this structure each of the weights 49 produces a moment about the horizontal axis 48 to apply a continual tension to the filament 43.

When the filament 43 expands the weight 49 is lowered and moved horizontally away from the axis 48 whereby the moment of the weight 49 about axis 48 increases to increase the tension on the filament 43,

The channel member 45 is secured by means of insulators 51 to a mounting plate 52 from which are supported anode plates 53, a portion of which project forwardly of the longitudinal opening 46 in the channel member 45 for accelerating and directing the electrons initiated from the filaments 31 onto the material therebelow. The filaments 43 are heated by current directed therethrough by means of leads 54 connected to the support posts 44 and leads 55 connected to the rod stubs 43a.

While these and other details have been shown by Way of illustration and example for the purpose of clarity of understanding, it is understood that certain changes and modifications can be made within the spirit of the invention as limited by the scope of the appended claims.

What is claimed is:

1. In an electron gun the combination of a gun housing, an elongate cathode filament length mounted within said housing, means affixing one end of said filament to said housing, a lever arm mounted on said housing, one end of said lever arm having a moment of movement in axial alignment with said filament length, the other end of said filament being attached to the one end of said lever arm and weighted means connected to the other end of the lever arm to form a weighted bias for the arm biasing the one end of the arm away from the filament length to hold the filament length under tension said Weighted means being positoned in the vertical plane containing said filament and substantially entirely within the length of said filament.

2. In an electron gun the combination of a gun housing, an elongate cathode filament length, means affixing one end of said filament length to said housing, a lever arm rotatably mounted on said housing, one end of said lever arm having a moment of movement in axial alignment with said filament length, the other end of said filament length being attached to the one end of said lever arm, weighted means connected to the other end of said lever arm applying a continual tension to said filament length and including a weight and means rotatably mounting said weight on a horizontal axis, said weight being positioned above and to one side of said horizontal axis before said filament is put in use.

3. In an electron gun the combination of a gun housing, an elongate cathode filament length, means aflixing one end of said filament to said housing, weighted means connected to the other end of said filament length applying a continual tension to said filament length including a lever arm rotatably mounted on a horizontal axis, a weight connected to one end of said lever arm vertically above and to one side of said horizontal axis before said filament structure is expanded and means connecting the other end of said lever arm to the other end of said filament length whereby the moment of said Weight supports the other end of said filament structure and applies a continual tension to said filament structure, the amount of tension increasing as the filament initially expands.

4. The electron gun of claim 2 characterized further in that said weighted means is positioned in the vertical plane containing said filament length and substantially entirely within the length of said filament.

References Cited by the Examiner UNITED STATES PATENTS 3/1930 Ipsen 13-25 7/1954 Black et al 3l3--278 

1. IN AN ELECTRON GUN THE COMBINATION OF A GUN HOUSING, AN ELONGATED CATHODE FILAMENT LENGTH MOUNTED WITHIN SAID HOUSING, MEANS AFFIXING ONE END OF SAID FILAMENT TO SAID HOUSING, A LEVER ARM MOUNTED ON SAID HOUSING, ONE END OF SAID LEVER ARM HAVING A MOMENT OF MOVEMENT IN AXIAL ALIGNMENT WITH SAID FILAMENT LENGTH, THE OTHER END OF SAID FILAMENT BEING ATTACHED TO THE ONE END OF SAID LEVER ARM AND WEIGHTED MEANS CONNECTED TO THE OTHER END OF THE LEVER ARM TO FORM A WEIGHTED BIAS FOR THE ARM BIASING THE 